Transparent films effective in screening heat is advantageous to be associated with means for preventing malfunctions of integrated circuits or electronic components, or for reducing the costs for cooling and heating by lessening the amount of solar energy going in and out of rooms and automobiles through windows. In addition, it is possible to offer effects of screening infrared rays when they are applied to various products such as optical fibers, sun visors, PET vessels, packaging films, glasses, textile goods, peep holes of heaters, heating apparatuses, and so on.
There has been proposed several films, which is capable of transmitting light with the wavelength of 380˜780 nm in a visible right range while reflecting light with the wavelength of 800˜2500 nm around the range of infrared lays, formed by the methods of: (1) forming a film with ingredients of tin oxide and antimony oxide by means of a spray process (refer to JP03-103341); (2) forming a film of tin-doped indium oxide (hereinafter, “ITO”) on a glass substrate by means of physical vapor deposition, chemical vapor deposition, or sputtering; and (3) coating an near-infrared absorber in the type of organic dyestuffs, such as pthalocyannine series, anthraquinone series, naphtoquinone series, cyanine series, naphtaloctannine series, condensed azo polymers, and pyrrol series, on a substrate by means of an organic solvent and an organic binder, or transform the about-infrared absorber into a coating.
However, the method (1) needs a thick film because it has weak performance for screening heat rays, resulting in a low transmittance rate for visible light. The method (2) consumes a high product cost because it needs an apparatus with control of the atmosphere in high vacuum and accuracy, being restricted in sizes of coating films and shapes and disadvantageous to implementation due to insufficient mass-productivity. The method (3) is insufficient in advancing the heat cutoff efficiency because it has a low transmittance rate for visible light and dark colors and is restricted to absorb near-infrared rays with wavelengths 690˜1000 nm. While the methods (1) and (2) are available to cut off ultraviolet rays as well as heat rays, they are incapable of receiving electric waves from mobile phones, televisions, or radios, because their materials reflects the electric waves due to small surface resistance, i.e., high electrical conductance.
In order to overcome the problems, there have been proposed several techniques disclosed in Japanese Patent NOs. JP56-156606, JP58-117228, and JP63-281837, in which respectively an antimony-doped tin oxide (hereinafter, referred to as “ATO”) is mixed with a resin binder, ATO is directly added to a resin binder dissolved in an organic solvent, and a coating compound manufactured by adding an organic binder and tin oxide nanoparticles into a splittable surfactant is deposited to form a heat-ray cutoff film. But it still needs a thick film enough to perform an infrared ray cutoff function, which contains low transmittance rate for a visible light to lower the transparency.
On the other hand, Japanese Patent NOs. JP07-24957, JP07-70363, JP07-70481, JP07-70842, JP07-70445, and JP08-41441 disclose the methods in which; a powder with an excellent performance of screening heat rays is made by processing or manufacturing ITO nanoparticles in the atmosphere of inert gas; and a heat cutoff film formed by mixing organic/inorganic binders with a dispersion sol made from using water or an alcoholic solvent without using an organic solvent, capable of screening heat rays over 90% under the condition of wavelength 100 nm. However, as the ITO nanoparticles is ingredient of a highly expensive indium and obtained by processing twice in the atmosphere of inert gas, it is limited in practical implementation due to the high product cost. Moreover, the ITO nanoparticles cause delamination or cohesion when they are mixed with a ultraviolet-hardening resin binder and is in poor preservation.
Japanese Patent NOs. JP09-324144, JP09-310031, JP09-316115, JP09-316363, JP10-100310, and JP12-169765 propose the method of mixing a dispersion sol of the first heat-ray cutoff nanoparticles and the second heat-ray cutoff compound (the near-infrared absorber or 6-boronic nanoparticles), or mixing respective coating compounds. However, in this case, it has disadvantages that a visible ray transmittance rate is remarkably degraded or it is not easy to induce dispersion while manufacturing a dispersion sol of the second heat-ray cutoff compound, which disables a low cost mass-production for the heat-ray cutoff films.
Japanese Patent NOs. JP06-262717, JP06-316439, JP06-257922, JP08-281860, JP09-108621 and JP09-151203, and U.S. Patent Publication NO. 2002/0090507 disclose the methods of forming an organic solvent dispersion sol of an ATO water dispersion sol and an organic ATO (i.e., enhancing co-usability to an organic solvent by converting a hydrophilic surface of an ATO into a hydrophobic surface) and of forming heat-ray cutoff coating films respective to a hydrolic binder and an organic resin binder. However, the water ATO sol is insufficient in co-usability with an organic resin binder, and the organic ATO sol is insufficient in co-usability with a hydrolic resin binder. Further, the organic ATO sol needs a secondary process to change the hydrophilic surface into the hydrophobic surface, which causes an increase of the product cost.
Therefore, it is desired to develop an improved coating film having excellent property for cutting off heat rays.